Thermoplastic-based building panel comprising a balancing layer

ABSTRACT

A thermoplastic-based building panel, such as a floor panel. The building panel includes an upper layer arrangement, a lower layer arrangement, and a balancing layer provided between the lower and the upper layer arrangement. The building panel further includes a groove arrangement including grooves. A thermoplastic-based building panel including an upper layer arrangement and a balancing layer which is a bottom layer of the building panel. The building panel includes a groove arrangement, wherein a major portion of the grooves therein is provided in the balancing layer only. A thermoplastic-based building panel including a mechanical locking system for horizontally and/or vertically locking the building panel to an adjacent building panel. The mechanical locking system includes a cooperating surface which is situated in a balancing layer and is configured to cooperate with a cooperating surface of an adjacent building panel.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of Swedish Application No.1951558-4, filed on Dec. 27, 2019 and Swedish Application No. 1951559-2,filed on Dec. 27, 2019. The entire contents of each of SwedishApplication No. 1951558-4 and Swedish Application No. 1951559-2 arehereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The disclosure generally relates to balancing of a thermoplastic-basedbuilding panel, such as a floor panel. More specifically, the disclosurerelates to a thermoplastic-based building panel comprising a balancinglayer, wherein the balancing layer is provided between a lower and anupper layer arrangement or wherein the balancing layer is a bottom layerof the building panel. The disclosure also relates to athermoplastic-based building panel comprising a mechanical lockingsystem for horizontal and/or vertical locking comprising a cooperatingsurface that is at least partially situated in a balancing layer.Optionally, the building panel may comprise at least one groove.

BACKGROUND

Panels comprising a thermoplastic material, such as Luxury Vinyl Tiles(LVT panels) or Stone Plastic (Polymer) Composite panels (SPC panels)present many advantages, such as high durability and easy maintenance. Atypical problem with these types of panels, however, is that they maybecome too heavy for some applications. Heavy panels may negativelyimpact their performance as well as their production and transportationcosts. Moreover, the transportation and the handling of the panels maybecome cumbersome. Therefore, there is currently a strong desire toreduce the weight of the panels, e.g., by using less material duringmanufacturing of the panels or by removing material from the panelsafter their formation. Less usage of material may also imply substantialcost savings.

WO 2013/032391 and WO 2014/007738 disclose panels comprising athermoplastic material and being provided with a certain groovestructure for decreasing their weight. A similar panel comprisingcertain grooves 10 in a rear side 5 of the panel 1 is illustrated in across-sectional side view in FIG. 1 a.

An LVT panel or an SPC panel typically has a layered structure, eachlayer exhibiting a different function. For example, the panel may have awear layer, a print film and a core. A bottom layer of the panel may bea balancing layer or a backing layer which may ensure that the panelremains sufficiently flat under ambient temperature variations.Typically, the balancing layer mainly comprises a thermoplastic materialand a filler. However, the grooves described above may generically havea negative impact on the balancing of the known panels, which indeed maybecome dimensionally unstable under ambient temperature variations. Atleast for some panels, a balancing layer completely penetrated bygrooves may not contribute sufficiently to the balancing of the panel.As shown in FIG. 1b , an unbalanced panel 1 may curl, e.g., such thatthe front side and the rear side become concave. It is generally desiredthat the layers of the panel, such as the top layer, the core and thebalancing layer, expand and contract substantially in a similar mannersuch that the panel remain sufficiently flat under temperaturevariations.

SUMMARY

It is therefore an object of at least embodiments of the presentdisclosure to provide a thermoplastic-based building panel, such as afloor panel, having a reduced weight and/or a reduced material contentwith improved balancing properties.

It is also an object of at least embodiments of the present disclosureto provide a thermoplastic-based building panel that is more resistantto curling effects, which may be induced by ambient temperaturevariations, and/or that is more resistant to indentation effects.

It is also an object of at least embodiments of the present disclosureto provide a more robust and/or stronger mechanical locking system of athermoplastic-based building panel. At least some of these and otherobjects and advantages that will be apparent from the description havebeen achieved by the various aspects described below.

In accordance with a first aspect of the disclosure, there is provided athermoplastic-based building panel, such as a floor panel, comprising anupper layer arrangement comprising at least one upper layer, a lowerlayer arrangement comprising at least one lower layer, and a balancinglayer provided between the lower layer arrangement and the upper layerarrangement. The building panel further comprises a groove arrangementcomprising at least one groove, preferably a plurality of grooves.

By having a balancing layer that is displaced from a rear side of thebuilding panel, less material or even no material may have to be removedfrom the balancing layer when providing grooves in the building panel,such as in a bottom portion thereof. Thereby, the balancing layer mayremain more intact and the balancing of the building panel may becomeimproved. Moreover, the curling effect of the building panel may becomereduced. Generally in this disclosure, in particular for the firstaspect as well as for the second aspect introduced below, the curlingand/or the balancing of the panel may be determined by ISO 23999:2018and/or by utilizing an Indicator Method detailed in an “Examples”section below. The thermoplastic-based panel may be sufficientlybalanced up to temperatures of 60° C., or even up to 80° C. Anadditional advantage of a more intact layer assembly is that the panelmay become more resistant to indentation effects. Generally in thisdisclosure, in particular for the first and second aspects, a residualindentation may be determined by means of the standard ASTM F1914-18(product specification ASTM F1700).

The building panel, or panel for short, may be a floor panel, a wallpanel, a ceiling panel or a furniture panel. In non-limiting examples,the floor panel may be an LVT tile, an SPC panel, an EPC panel (ExpandedPolymer Core), or a WPC (Wood Plastic Composite) panel. Moreover, thepanel may comprise a pair of opposite edge portions, such as a firstpair and a second pair of opposite edge portions. The first pair and thesecond pair may comprise long edge portions and short edge portions ofthe panel, respectively.

The panel may comprise a front side and a rear side and may extend in afirst X and a second Y horizontal direction, which preferably areperpendicular to each other. In a first example, the first and secondhorizontal directions extend in parallel with long and short edgeportions, respectively. In a second example, the first and secondhorizontal directions extend in parallel with short and long edgeportions, respectively. A vertical direction Z of the panel may beperpendicular to the first and second horizontal directions and may beparallel with a thickness direction of the panel. Thereby, we may referto elements being arranged “above” or “below” each other. The front sidemay be adapted to be visible and, at least in some embodiments, such asfor a floor panel, the rear side may be adapted to be concealed in aninstalled state of the panel. Indeed, a set of building panels, such asfloor panels, may be installed on a substructure, such as a subfloor.

The at least one groove may have a longitudinal extension and atransverse extension. The longitudinal extension may be larger than thetransverse extension. In a first example, the longitudinal and thetransverse extensions may be parallel to a long and a short edgeportion, respectively. In a second example, the longitudinal and thetransverse extensions may be parallel to a short and a long edgeportion, respectively.

The upper layers may be laminated to each other and/or bonded to eachother by an adhesive. Likewise, the lower layers may be laminated toeach other and/or bonded to each other by an adhesive. The upper and/orthe lower layer arrangement may be laminated to the balancing layerand/or bonded thereto by an adhesive. Any of said layers or layerarrangements herein may be laminated to each other under heat andpressure. In the second aspect introduced below, reference willtypically be made only to an upper layer arrangement and not a lowerlayer arrangement.

The groove arrangement may be provided in the lower layer arrangement.

The at least one groove may be provided in a rear side of the lowerlayer arrangement, preferably in a bottom layer thereof.

The groove arrangement may be post-formed after forming the panel perse, preferably by removing material from a bottom layer, such as a lowerlayer, of the panel. An ordinarily skilled artisan will appreciate that,within the scope of the present disclosure, the concept of being“post-formed” includes the case when the groove arrangement ispost-formed after forming a board per se and thereafter dividing theboard into at least one panel, such as a plurality of panels. Preformedgrooves are equally conceivable.

The at least one groove may be tapering towards a depth direction of thegrooves, which may be parallel with the vertical direction of the panel.Generally, an inner portion of the grooves may be curved or planar.

In some embodiments, each of the at least one groove may be an internalgroove provided within the lower layer arrangement, such as in a bottomlayer thereof. Thereby, an internal groove may have walls within thepanel along one horizontal direction and along the vertical direction.The internal groove may be open towards the other horizontal direction.

A groove depth, preferably a maximal groove depth, of the at least onegroove may be larger than 20%, such as larger than 30% or larger than40%, of a thickness of the lower layer arrangement and/or of a thicknessof the building panel, such as floor panel.

Generally, the balancing layer may be at least partly provided above thegroove arrangement, such as entirely above the groove arrangement.

A major portion of the grooves may be provided entirely below thebalancing layer. Thereby, a major portion of the grooves does not extendinto, such as penetrate, the balancing layer. For example, the groovesmay penetrate the lower layer arrangement only.

Generally herein, the major portion of the grooves may comprise a majorportion of a total volume of the grooves and/or a major portion of atotal number of grooves. Hence, a major portion of the total volume ofthe grooves and/or a major portion of the total number of grooves may beprovided entirely below the balancing layer.

The major portion may be at least 50% of the number of grooves and/or atleast 50% of the total volume of the grooves. When the grooves areprovided in the rear side, the total volume of the grooves may be avolume occupied by the grooves within the panel and being limited by ahorizontal plane HP provided along the rear side. When the grooves areinternal grooves, the total volume of the grooves may be a volumeoccupied by the grooves within the panel and being limited by a verticalplane VP, preferably provided along the edge portions.

In some embodiments, an average groove depth of a plurality of groovesmay be smaller than a thickness of the lower layer arrangement. Hence,an average value of an innermost portion of the grooves along thevertical direction may be provided below the balancing layer. Theseembodiments provide examples of the major portion of the grooves beingprovided entirely below the balancing layer.

In some embodiments, all grooves are provided entirely below thebalancing layer.

The building panel may comprise a plurality of grooves in the lowerlayer arrangement, wherein an innermost portion of at least one grooveis separated from the balancing layer by a distance in the verticaldirection of the building panel. Thereby, the lower layer arrangementmay be continuous, which may improve the balancing of the panel. Forexample, there may be a distance between each of the plurality ofgrooves and the balancing layer. The distance may be at least 0.3 mm,such as at least 1 mm. Preferably, the distance is non-negative,although in alternative embodiments the distance between the grooves andthe balancing layer is negative, such that the grooves extend throughthe balancing layer. The distance may be larger than 0.25 times athickness of an uppermost layer of the upper layer arrangement,preferably larger than 0.50 times or larger than 1.0 times the thicknessof the uppermost layer. For example, the uppermost layer may be a wearlayer.

A combined thickness, such as a maximal combined thickness, of the lowerlayer arrangement and the balancing layer, may be at least 20%, such asat least 35% or at least 50%, of a thickness of the building panel.

A thickness of the balancing layer may be smaller than a groove depth,preferably a maximal groove depth, of the at least one groove.

Generally herein, the maximal groove depth of a groove may be a distancefrom the rear side of the building panel to the innermost portion of thegroove. The groove depth may be a distance along the vertical directionof the building panel. Moreover, for an internal groove, the maximalgroove depth may be a maximal vertical distance between walls of theinternal groove.

A thickness, such as a maximal thickness, of the balancing layer may beat least 5%, such as at least 10% or at least 20%, of a thickness of thebuilding panel. In some embodiments, the thickness of the balancinglayer may even be at least 30% of the thickness of the building panel.

A thickness, such as a maximal thickness, of the balancing layer may belarger than a thickness of an upper layer of the upper layerarrangement, wherein the upper layer preferably is an uppermost layer ofthe upper layer arrangement. For example, the uppermost layer may be awear layer. Thereby, an improved balancing of the panel may be provided.A thickness, such as a maximal thickness, of the balancing layer, mayhave at least the same thickness as the uppermost layer, preferablybeing larger. In some embodiments, a thickness, such as a maximalthickness, of the balancing layer may be at least 5 times or at least 10times, a thickness, such as a maximal thickness, of the uppermost layer,such as a wear layer.

In accordance with a second aspect of the disclosure, there is provideda thermoplastic-based building panel, such as a floor panel, comprisingan upper layer arrangement comprising at least one upper layer, and abalancing layer which is a bottom layer of the building panel. Thebuilding panel further comprises a groove arrangement comprising atleast one groove, preferably a plurality of grooves, wherein a majorportion of the grooves are provided in the balancing layer only.

In accordance with the second aspect, a major portion of the groovesdoes not penetrate into other layers of the building panel and thebalancing layer may remain more intact. Thereby, an improved balancingof the panel may be provided. Moreover, the curling effect of thebuilding panel, such as induced by ambient temperature variations, maybecome reduced. Incidentally, it is noted that a minor portion of thegrooves may optionally penetrate into the upper layers of the buildingpanel.

Generally herein, a minor portion and the major portion may jointlycorrespond to all of the grooves, such as the total number of groovesand/or the total volume of the grooves.

The upper layers may be laminated to each other and/or bonded to eachother by an adhesive. The upper layer arrangement may be laminated tothe balancing layer and/or bonded thereto by an adhesive.

In some embodiments, all of the grooves are provided in the balancinglayer only. Thereby, the bottom layer may be continuous, without anygrooves penetrating both a lower side and an upper side thereof.

A groove depth, preferably a maximal groove depth, of the groove(s) maybe larger than 20%, such as larger than 30% or larger than 40%, of athickness of the balancing layer and/or of a thickness of the buildingpanel, such as floor panel.

In some embodiments, an average groove depth of a plurality of groovesmay be smaller than a thickness of the balancing layer. Hence, anaverage value of an innermost portion of the grooves along the verticaldirection may be provided below the upper layer arrangement. Theseembodiments provide examples of the major portion of the grooves beingprovided entirely below the upper layer arrangement.

The grooves may be provided in a rear side of the balancing layer.

In some embodiments, each of the at least one groove may be an internalgroove provided at least partially, preferably completely, within thebalancing layer. Thereby, an internal groove may have walls within thepanel along one horizontal direction and along the vertical direction ofthe panel. The internal groove may be open towards the other horizontaldirection.

The major portion may comprise a major portion of a total volume of thegrooves and/or a major portion of a total number of grooves. In someembodiments, the major portion of the grooves may comprise a majorportion of a groove depth. Hence, a major portion, such as at least 50%,of the innermost portions of the grooves may be provided entirely belowthe balancing layer.

The major portion may be at least 50% of the number of grooves and/or atleast 50% of the total volume of the grooves. In some embodiments, thetotal volume of the grooves may be at least 60% or even at least 70% ofthe total volume of the grooves. Embodiments of the total volume of thegrooves have been described in relation to the first aspect, wherebyreference is made thereto by analogy. The major portion of the totalnumber of the grooves may be more than 50% of the total number ofgrooves. In non-limiting examples, a major portion of 11 grooves is atleast 6 grooves and a major portion of 14 grooves is at least 8 grooves.The embodiments relating to a “major portion” are valid also for thefirst aspect by analogy.

A thickness, such as a maximal thickness, of the balancing layer may belarger than a thickness of an upper layer of the upper layerarrangement, wherein the upper layer preferably is an uppermost layer ofthe upper layer arrangement. For example, the uppermost layer may be awear layer. A thickness, such as a maximal thickness, of the balancinglayer, may be at least 4 times, such as at least 10 times or at least 20times, a thickness, such as a maximal thickness, of the uppermost layer,such as a wear layer.

A thickness, such as a maximal thickness, of the balancing layer may beat least 20%, such as at least 35% or at least 50%, of a thickness ofthe building panel. Such a relatively thicker balancing layer mayrequire more material content and may become more costly. However, byusing a recyclable material, such as a thermoplastic polymer, in thebalancing layer, material that is removed or saved when forming thegrooves may be recycled or reused. Hence, the cost, such as a totalproduction cost of several panels, may effectively be reduced.

The building panel may comprise a plurality of grooves in the balancinglayer, wherein an innermost portion of at least one groove is separatedfrom the upper layer arrangement by a distance in the vertical directionof the building panel. Thereby, the balancing layer may be continuous,which may improve the balancing of the panel. For example, each of theplurality of grooves may be separated from the upper layer arrangement.The distance may be at least 0.3 mm, such as at least 1 mm. The distancemay be larger than 0.25 times a thickness of an uppermost layer of theupper layer arrangement, preferably larger than 0.50 times or largerthan 1.0 times the thickness of the uppermost layer. For example, theuppermost layer may be a wear layer.

It is emphasized that the following embodiments are conceivable for apanel in accordance with any of the first and second aspects.

In some embodiments, a groove depth of a plurality of grooves may beessentially the same.

The building panel may comprise a plurality of grooves, wherein a groovedepth, preferably a maximal groove depth, of at least two grooves aredifferent.

In some embodiments, the groove arrangement may comprise a calibratinggroove, for example as described in WO 2014/182215, page 2, lines 13-22which hereby is incorporated by reference in its entirety.

Generally, the balancing layer may be a discontinuous layer. Thereby,the balancing layer may be fully penetrated, such as by at least onegroove or even all grooves. Such a panel may be less balanced comparedto a panel where the balancing layer is continuous, but may besufficiently balanced for some applications. Optionally, the panel insuch embodiments may comprise a reinforcement element, see thediscussion below.

The balancing layer may be a continuous layer. According to thisembodiment, the balancing layer is not fully penetrated, such as by thegrooves. Thereby, the panel may become better balanced. In a firstexample, the balancing layer has a substantially constant thickness,optionally comprising internal grooves. In a second example, thebalancing layer has a varying thickness along a first and/or a secondhorizontal direction of the building panel. The varying thickness mayresult from grooves being provided at least partly in the balancinglayer.

The building panel may comprise at least one reinforcement element, suchas at least one glass-fibre layer. The upper and/or lower layerarrangement may comprise a reinforcement element, such as a glass-fibrelayer. Moreover, the balancing layer may comprise a reinforcementelement, such as a glass-fibre layer. In some embodiments, thereinforcement element may contribute to the balancing of the panel.

The at least one reinforcement element may be provided in a centreportion of the building panel, wherein the centre portion is providedbetween an innermost portion of the grooves and the front side in thevertical direction of the panel. The centre portion may be provided at adistance from the front side of between 35% and 65% of a distancebetween the innermost portion and the front side.

The building panel, such as a floor panel, may further comprise amechanical locking system in an edge portion or edge portions forhorizontally and/or vertically locking the building panel to an adjacentbuilding panel or adjacent building panels. The panel may comprise amechanical locking system on the long edge portions and/or on the shortedge portions.

In some embodiments, the building panel is not provided with anymechanical locking system. Instead, the panel may be embodied as a floorpanel which may be configured to be installed loosely on a subfloor orit may be embodied as a building panel, such as a floor panel,configured to be nailed or glued to a substructure, such as a subfloor.

Embodiments of the mechanical locking system of the first or the secondaspect may be implemented in accordance with any embodiment describedherein in relation to the third aspect.

Generally herein, a panel thickness may be 2-40 mm, such as 2-10 mm or3-6 mm. For example, when the thickness of the lower layer arrangementin the first aspect or the balancing layer in the second aspect is 2-30mm, a groove depth of any of the grooves may be at least 0.5-10 mm. Forexample, a floor panel having a thickness of 2-10 mm may have groovedepth which is at least 0.5-5 mm.

It is noted that in any of the first and second aspects, a separatelyformed underlay element may at least partially, preferably entirely,cover the rear side of the panel. The underlay element may be a foam,such as irradiated cross-linked polyethylene foam (IXPE) or EthyleneVinyl Acetate foam (EVA), or cork. The underlay element may be bonded tothe rear side by an adhesive according to principles known in the art.

In accordance with a third aspect of the disclosure, there is provided athermoplastic-based building panel, such as a floor panel, comprising anupper layer arrangement and/or a lower layer arrangement, a balancinglayer comprising a thermoplastic polymer, and a mechanical lockingsystem for horizontally and/or vertically locking the building panel toan adjacent building panel. The mechanical locking system comprises acooperating surface provided in an edge portion of the building paneland being configured to cooperate with a cooperating surface of theadjacent building panel, wherein the cooperating surface of themechanical locking system is at least partially situated in thebalancing layer.

For many thermoplastic-based panels, a part of the mechanical lockingsystem may be the weakest part of the panel, for example when subject tohigh stress, e.g., when conducting a high-load test, a locking strengthtest or a Castor chair test, or during installation of the panels. Amechanical locking system in accordance with the third aspect may becomemore robust and/or stronger. For example, the risk of damaging, e.g.,cracking, a part of the mechanical locking system may be reduced.

The cooperating surfaces, such as locking surfaces and/or guidingsurfaces, may cooperate by direct engagement or indirectly. In anyembodiment described herein, there may be a sealing agent, such as a waxor an adhesive, provided between the cooperating surfaces, therebyproviding examples of an indirect engagement.

The cooperating surface may be a horizontal and/or vertical cooperatingsurface for horizontal and/or vertical cooperation, such as locking tothe adjacent panel and/or guiding of the adjacent panel.

The balancing layer may be provided between the lower layer arrangementand the upper layer arrangement. Embodiments and examples may be thesame as those of the first aspect, whereby reference is made thereto.

The balancing layer may be a bottom layer of the building panel.Embodiments and examples may be the same as those of the second aspect,whereby reference is made thereto.

The balancing layer may at least partially extend through a lockingelement provided on a strip and/or through a locking groove, wherein thelocking element is configured to engage with a locking groove of theadjacent building panel for horizontal locking. The strip may extendhorizontally beyond an upper edge of the edge portion. Generally, theupper edges of the panels may be juxtaposed in a locked state of thepanels. When a normal of surface portions of the upper edges arearranged perpendicularly to a normal of the front and/or rear sides ofthe panels, they may define a vertical plane VP, preferably having anormal being parallel with the normal of the surface portions.

The balancing layer may at least partially extend through an upperportion, an inner wall and/or an outer wall of the locking elementand/or through an upper wall, an inner wall and/or an outer wall of thelocking groove,

Generally herein, the edge portion may be a short edge portion and/or along edge portion.

The cooperating surface may be situated on the locking element and/or inthe locking groove, for example at least partially in the balancinglayer.

An uppermost surface of the locking element may comprise a portion ofthe balancing layer, wherein the cooperating surface preferably isprovided in the uppermost surface.

The balancing layer may at least partially extend along a strip, such asalong an upper portion of the strip. The strip may be embodied asdescribed above.

An uppermost surface of the strip, for example provided horizontallyinwardly of the locking element, may comprise a portion of the balancinglayer. The cooperating surface may be provided in the uppermost surface.

A transitional surface transitioning from the uppermost surface of thestrip to the locking element, such as an inner wall of the lockingelement, may comprise a portion of the balancing layer. Thereby, themechanical locking system may become stronger and/or more robust, forexample when subject to high stress, e.g., when conducting a lockingstrength test, or during installation of the panels. Indeed, a regionaround the transitional surface may be exposed to particularly highstresses, especially on a short edge portion. Optionally, thetransitional surface may comprise a portion of the uppermost surface ofthe strip and/or a portion of the inner wall of the locking element.

The balancing layer may at least partially extend through a tongueportion, such as through a lower portion of the tongue portion, whereinthe tongue portion is configured to engage with a tongue groove of theadjacent building panel for vertical locking.

The tongue portion may comprise a tongue that is integrally formed withthe panel.

The tongue portion may comprise a separate, and preferably flexible,tongue that is configured to be provided in a displacement grooveprovided at an edge portion of the panel, preferably a short edgeportion.

The cooperating surface may be at least partially provided in a wall ofthe tongue groove, such as in at least one of an upper wall, a lowerwall and an inner wall of the tongue groove.

The cooperating surface may be situated on the tongue portion.

A lowermost surface of the tongue portion may comprise a portion of thebalancing layer, wherein the cooperating surface preferably is providedin the lowermost surface.

The cooperating surface may be a first cooperating surface provided in afirst edge portion of the building panel and the mechanical lockingsystem may further comprise a second cooperating surface provided in asecond edge portion of the building panel, the first and second edgeportions preferably being oppositely arranged on the building panel,wherein the second cooperating surface is at least partially situated inthe balancing layer.

Generally, the first and second cooperating surfaces may be arranged tocooperate with a corresponding second and first cooperating surface of arespective adjacent building panel. The cooperating surface of theadjacent building panel may be a general cooperating surface.Optionally, however, the cooperating surface of the adjacent buildingpanel may be at least partially situated in the balancing layer of theadjacent building panel.

The cooperating surface may be a locking surface configured to engagewith a locking surface of the adjacent building panel in a locked stateof the building panel and the adjacent building panel. The lockingsurfaces may engage for vertical and/or horizontal locking. Hence, thelocking surfaces may be vertical locking surfaces and/or horizontallocking surfaces. The locking surface of the adjacent building panel maybe a general locking surface. Optionally, however, the locking surfaceof the adjacent building panel may be at least partially situated in thebalancing layer of the adjacent building panel.

The cooperating surface may be a guiding surface configured to guide theadjacent building panel during locking of the building panel to theadjacent building panel, such as by cooperating or engaging with acooperating surface, such as a guiding surface, of the adjacent buildingpanel during locking. The guiding surface may guide the adjacent panelvertically and/or horizontally. The cooperating surface, such as aguiding surface, of the adjacent building panel may be a generalcooperating surface. Optionally, however, the cooperating surface of theadjacent building panel may be at least partially situated in thebalancing layer of the adjacent building panel.

The adjacent building panel may be configured to be angled downwardsand/or displaced vertically downwards towards the building panel duringlocking. Alternatively, however, the building panel may be configured tobe angled downwards and/or displaced vertically downwards towards theadjacent building panel during locking. Indeed, an ordinarily skilledartisan will appreciate that, within the scope of the presentdisclosure, the roles of the building panel and the adjacent buildingpanel described herein may be interchanged. For example, the features ofthe cooperating surfaces, such as the locking surfaces and/or guidingsurfaces, may be interchanged. In particular, the adjacent buildingpanel may comprise a mechanical locking system for horizontally and/orvertically locking the adjacent building panel to a building panel, themechanical locking system comprising a cooperating surface provided inan edge portion of the adjacent building panel and being configured tocooperate with a cooperating surface of the building panel. Thecooperating surface may be at least partially situated in the balancinglayer of the adjacent building panel. For simplicity, however, referencewill often be made only to a cooperating surface being at leastpartially situated in the balancing layer of the building panel.

In some embodiments, the cooperating surface may be a locking surface aswell as a guiding surface.

The building panel may further comprise a groove arrangement comprisingat least one groove, preferably a plurality of grooves. The grooves maybe embodied as in any of the first or second aspects, whereby referenceis made thereto.

When the panel is subject to high stress and/or is largely curled, aninner portion of the grooves may be the weakest portion of the panel. Byhaving a layer, such as a lower layer or a balancing layer, comprising athermoplastic polymer, the inner portion may be more flexible and/orless brittle. As a result, the inner portion, and hence the panel as awhole, may become more resistant to high stress.

Other embodiments and examples of the building panel in accordance withthe third aspect may be largely analogous to those of the first or thesecond aspect, whereby reference is made to the above. In particular,embodiments and examples of at least one selected from the group of thegrooves, the upper and/or the lower layer arrangements, the balancinglayer and the thicknesses may be the same. It is emphasized, however,that a groove arrangement is optional for the building panel inaccordance with the third aspect.

It is stressed that the following embodiments relating to the materialcomposition and properties of the balancing layer as well as the upperand/or the lower layer arrangement are applicable for each of the first,second and third aspects.

The upper layer arrangement, such as each of the at least one upperlayer, may comprise a thermoplastic polymer and, optionally, a filler.

The upper layer arrangement may comprise a wear layer and/or a printlayer, such as a print film. Preferably, the wear layer is an uppermostlayer. The print layer may be provided below the wear layer. It isunderstood that, generally, a coating, such as a UV curable coating, maybe provided on the upper layer arrangement, such as on the uppermostlayer, preferably being a wear layer. For sake of clarity, such acoating will often be left out in this disclosure, but may be implicitlyunderstood to be included.

The balancing layer may comprise a thermoplastic polymer and,optionally, a filler.

The lower layer arrangement, such as each of the at least one lowerlayer, may comprise a thermoplastic polymer and, optionally, a filler.

The thermoplastic polymer of the upper and/or the lower layerarrangement may comprise polyvinyl chloride (PVC), polyethylene (PE),polyethylene terephthalate (PET), polypropylene (PP), acrylonitrilebutadiene styrene (ABS) or thermoplastic polyurethane (TPU).Additionally, or alternatively, the balancing layer may comprise PVC,PE, PET, PP, ABS or TPU. For example, the amount of the thermoplasticpolymer in each upper and/or lower layer and/or the balancing layer maybe 10-70 wt %, such as 20-50 wt %.

Generally, a filler of the upper and/or lower layer arrangement and/orof the balancing layer may comprise an organic filler and/or aninorganic filler. The filler may be a functional filler and/or anextender. The inorganic filler may be a mineral material, such ascalcium carbonate (CaCO₃) or stone material, such as stone powder, orsimilarly. The organic filler may be organic fibers, e.g., wood flour orrice husks. The filler may also be a clay material, such as kaolin. Forexample, the amount of filler in each upper and/or lower layer and/orthe balancing layer may be 20-90 wt %, such as 40-80 wt %.

Optionally, any, a pair, or each of the upper layer arrangement, thelower layer arrangement and the balancing layer may comprise aplasticizer and/or additives, such as a stabilizer, an impact modifier,a pigment, or a lubricant. Yet optionally, the upper and/or lower layerarrangement may comprise a foaming agent. Generally, the panel may be aresilient panel or a rigid panel, for example by virtue of comprising aplasticizer and by not comprising any plasticizer, respectively.Similarly, the upper or lower layer(s), or the balancing layer, may beresilient or rigid, for example depending on the presence of aplasticizer. In a preferred embodiment, the balancing layer may beresilient, thereby comprising a plasticizer. Thereby, the balancingproperty of the panel may be strengthened.

Generically herein, the concept of “material composition” may include atleast one of an amount and a type of a thermoplastic polymer, an amountand a type of a filler, an amount and a type of plasticizer and/oradditives, etc.

At least two layers of the panel, such as at least one upper layerand/or at least one lower layer, may have the same materialcompositions.

In some embodiments, the upper layer(s) and the balancing layer, as wellas the lower layer(s) in the first aspect, may comprise differentmaterial compositions. For example, each upper layer, the balancinglayer, as well as the lower layer(s) in the first aspect, may comprise athermoplastic polymer and, preferably, a filler.

In some embodiments of the first aspect, an upper layer and a lowerlayer may comprise a substantially similar material composition. Forexample, the upper layer and the lower layer may comprise athermoplastic polymer and preferably a filler.

In some embodiments of the first and the second aspects, an upper layerand the balancing layer may comprise a substantially similar materialcomposition. For example, the upper layer and the balancing layer maycomprise a thermoplastic polymer and preferably a filler.

An amount of a thermoplastic polymer in the balancing layer may behigher than an amount of a thermoplastic polymer in the upper and/orlower layer arrangement. For example, the amounts may be specified inweight percentages or volume percentages or, for example when thethermoplastic polymer is PVC, in parts per hundred of PVC resin (PHR).Optionally, an amount of a filler, such as a mineral filler, in thebalancing layer may be lower than an amount of a filler in the upperand/or lower layer arrangement. By this embodiment, the balancing layermay become less brittle and/or more flexible. Moreover, a strength, suchas a tensile strength, of the balancing layer may become higher. Thismay be advantageous, e.g., when the cooperating surface is at leastpartially situated in the balancing layer in accordance with the thirdaspect. For example, the mechanical locking system may become evenstronger and/or more robust. It is noted that a lower degree of a fillerin a layer, especially a mineral filler, may make the layer lessbrittle.

An amount of a thermoplastic polymer in the balancing layer may behigher than an amount of a thermoplastic polymer in each of the upperand/or lower layers. Generally herein, the panel may comprise an upperand a lower layer arrangement (first aspect), an upper layer arrangement(second aspect), or any combination of upper and/or lower layerarrangement(s) (third aspect). Optionally, an amount of a filler, suchas a mineral filler, in the balancing layer may be lower than an amountof a filler in each of the upper and/or lower layers.

Generally, a first layer of the panel comprising a higher amount of athermoplastic polymer, such as a wear layer or a balancing layer, andoptionally a lower amount of a filler, than a second layer of the panel,may contribute more to the curling of the panel, e.g., since athermoplastic polymer, such as PVC, may have a much higher coefficientof linear thermal expansion compared to a filler, such as CaCO₃. Forexample, the first layer may be the balancing layer or a wear layer andthe second layer may be an upper or a lower layer.

At least one upper and/or lower layer of the building panel may beextruded, such as coextruded. Preferably, each extruded or coextrudedlayer comprises a thermoplastic polymer.

The balancing layer may be extruded per se, or it may be coextruded withat least one upper and/or lower layer. For example, the panel maycomprise an AB, ABA or ABC coextruded layer element comprising two orthree layers. The balancing layer may be provided between an upper layerand a lower layer in an ABA or ABC coextruded layer element. Here, thesame letter (A) and different letters (A, B or C) refer to the layershaving substantially the same material composition and differentmaterial compositions, respectively.

In some embodiments, the upper and/or the lower layer arrangement maycomprise a non-polymeric layer. In a first example, a veneer may bebonded to an upper layer, which preferably is a layer comprising athermoplastic polymer, and preferably a filler. In a second example, apaper, preferably a melamine-formaldehyde impregnated paper, may bebonded to an upper layer, which preferably is a layer comprising athermoplastic polymer, and preferably a filler.

In accordance with a fourth aspect of the disclosure, there is provideda panel assembly comprising a building panel and an adjacent buildingpanel. The building panel and/or the adjacent building panel may beembodied as the building panel according to any of the embodiments andexamples of the first, second and third aspects, whereby reference ismade thereto.

Further aspects of the disclosure and embodiments and examples of eachof the first, second, third and fourth aspects are provided in anillustrative embodiment section below. It is emphasized that theembodiments and examples of any aspect may be combined with embodimentsand examples of any other aspect.

Generally, all terms used in the claims and items are to be interpretedaccording to their ordinary meaning in the technical field, unlessexplicitly defined otherwise herein. All references to “a/an/the[element, device, component, means, step, etc.]” are to be interpretedopenly as referring to at least one instance of said element, device,component, means, step, etc., unless explicitly stated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will in the following be described in connection toexemplary embodiments and in greater detail with reference to theappended exemplary drawings, wherein:

FIGS. 1a-1b illustrate in cross-sectional side views an embodiment of afloor panel comprising grooves according to known art and an embodimentof a curled floor panel.

FIGS. 1c-1e illustrate exemplary embodiments of a building panelaccording to the first aspect in a perspective view (FIG. 1c ), a bottomview (FIG. 1d ) and a cross-sectional side view (FIG. 1e ).

FIGS. 2a-2d illustrate exemplary embodiments of a budding panelaccording to the first aspect in cross-sectional side views.

FIGS. 3a-3c illustrate exemplary embodiments of a building panelaccording to the second aspect in cross-sectional side views (FIGS.3a-3b ) and a bottom view (FIG. 3c ).

FIGS. 4a-4c illustrate exemplary embodiments of a building panelaccording to the second aspect in cross-sectional side views.

FIGS. 5a-5d illustrate exemplary embodiments of a building panelaccording to the first and second aspects in cross-sectional side views(FIGS. 5a-5b ) and in a perspective view (FIG. 5c ) as well as anembodiment of a lower layer arrangement in a cross-sectional side view(FIG. 5d ).

FIGS. 6a-6c illustrate exemplary embodiments of a building panelcomprising a mechanical locking system in a bottom view (FIG. 6a ), across-sectional top view (FIG. 6c ) and in cross-sectional side views(FIGS. 6b-6c ).

FIGS. 7a-7f illustrate exemplary embodiments of a budding panelcomprising a mechanical locking system and locking of building panels incross-sectional side views and in zoomed-in cross-sectional side views.

FIGS. 8a-8d illustrate exemplary embodiments of a building panelcomprising a mechanical locking system in cross-sectional side views.

FIGS. 9a-9b illustrate in cross-sectional side views exemplaryembodiments of building panels comprising a mechanical locking systemand their locking.

FIGS. 9c-9e illustrate an exemplary indicator device which may implementthe Indicator Method described herein.

FIGS. 10a-10c show a photo of a sample exemplary reference panel andphotos of sample exemplary panels according to the first aspect showingthe curling effect under certain temperature variations.

FIG. 10d shows a photo of a sample exemplary reference panel.

FIGS. 11a-11d show photos of sample exemplary panels according to thefirst and second aspects showing the curling effect and a photo of asample exemplary reference panel.

FIGS. 12a-12d show photos of sample exemplary panels according to thefirst aspect subjected to residual indentation tests.

DETAILED DESCRIPTION

The various aspects of the disclosure will hereinafter be described withrespect to a thermoplastic-based floor panel, but an ordinarily skilledartisan will appreciate that, within the scope of the presentdisclosure, they are applicable for a general building panel, such as awall panel, a ceiling panel or a furniture panel. Therefore, in thefollowing, reference will often be made simply to a panel.

FIGS. 1c-1e, 2a-2d, 5a, 5c, 6a-6c, 7a-7c, 8a -8 b, 8 d and 9 a,illustrate embodiments of a thermoplastic-based panel 1 in the form of afloor panel according to the first aspect. The panel comprises an upperlayer arrangement 2, a lower layer arrangement 3, and a balancing layer4 provided between the lower and the upper layer arrangement. Generally,the upper layer arrangement comprises at least one upper layer 2 a, 2 b,2 c and the lower layer arrangement comprises at least one lower layer 3a, 3 b. A groove arrangement 10 comprising at least one groove 11,preferably a plurality of grooves, is provided in the lower layerarrangement 3.

The upper layer arrangement 2 may comprise a wear layer and/or a printlayer. The wear layer may be the uppermost layer 2 a.

In some embodiments, the upper 2 and/or the lower 3 layer arrangementmay be laminated to the balancing layer 4. In turn, at least some upperlayers and/or lower layers may be laminated to each other. For example,the upper layer(s), the lower layer(s), and the balancing layer may beprovided as sheets or may be provided on rolls and may be laminated toeach other under heat and pressure. The sheets may be stacked on top ofeach other and, for example, may be laminated to each other in a hotpress or a multi-daylight static press. The layers provided on rolls maybe laminated to each other in a continuous process. In some embodiments,the balancing layer may be (co-)extruded with at least one upper and/orlower layer, such as with all upper and lower layers except for the wearlayer and/or the print layer.

As shown in, e.g., the embodiments in FIGS. 1c-1e, 2a-2d, 6a-6c and 7a ,the grooves 11 may be provided in a rear side 5 of the lower layerarrangement 3, preferably in a bottom layer 5′ thereof. For example, thegrooves may be post-formed after forming the panel per se by removingmaterial from the bottom layer 5′, such as by rotating saw blades,cutting, milling, scraping or carving. Alternatively, the grooves may bepre-formed while forming the panel, such as during heating and pressingof the panel.

However, as shown in the embodiment in FIGS. 5a and 5c , it isconceivable that the grooves may be provided within the lower layerarrangement, such as in a bottom layer 5′ thereof. In an illustrativeembodiment, the grooves are bounded by a panel portion located belowgrooves. Alternatively, the grooves may include an opening at abottom-facing surface of the panel 1. For example, these internalgrooves 11 may be pre-formed in the lower layer arrangement, such asbeing formed during manufacturing of the lower layer arrangement and/orthe panel, e.g., by (co-)extrusion. The internal grooves 11 may havewalls within the panel along one horizontal direction, such as thesecond horizontal direction Y shown in FIG. 5c , and a verticaldirection Z of the panel. Generally herein, a thickness direction may beparallel with the vertical direction Z of the panel. The internalgrooves may be open towards the other horizontal direction, such as thefirst horizontal direction X shown in FIG. 5c . Thereby, the internalgrooves may extend all the way the edge portions, such as the short edgeportions.

The balancing layer 4 may be at least partly provided above the groovearrangement 10. Thereby, the balancing layer may be continuous. This isillustrated, e.g., in the embodiments in FIGS. 1c, 1e, 2a, 2c-2d, 5a,5c, 6b-6c and 7a . As also shown in some of these figures, the balancinglayer 4 may be provided entirely above the groove arrangement.

It is also conceivable that all grooves 11 entirely penetrate thebalancing layer as shown in the embodiment in FIG. 2b , such that thebalancing layer 4 becomes discontinuous. However, such a panel 1 may beless balanced compared to a panel where the balancing layer is at leastpartly provided above the groove arrangement. Nevertheless, such a panelmay be sufficiently balanced for some applications. For example, areinforcement element 13 may be provided therein as described below.

As shown, e.g., in the embodiments in FIGS. 1c, 1e, 2c-2d, 5a, 5c and6b-6c , the balancing layer 4 may have a substantially constantthickness T4, preferably by having a panel wherein all grooves areprovided entirely below the balancing layer. The grooves may penetratethe lower layer arrangement 3 only.

It is also conceivable that the balancing layer 4 may have a varyingthickness T4 along a first X and/or a second Y horizontal direction ofthe panel. For example, as shown in, e.g., FIGS. 2a-2b and 7a , grooves11 may be provided at least partly in the balancing layer 4, therebyproviding a varying thickness along the second horizontal direction Y. Amajor portion of the grooves may be provided entirely below thebalancing layer as shown in, e.g., FIG. 2a . Optionally, the thicknessmay vary also along the first horizontal direction X, e.g., by havinggrooves provided inside the edge portions of the panel along the firsthorizontal direction X. This is conceivable for any of the embodimentsin, e.g., FIGS. 1c-1e, 2a-2d, 6a-6c and 7a -7 c.

The major portion may be at least 50% of the number of grooves and/or atleast 50% of the total volume TV of the grooves. The total volume TV ofthe grooves 11 provided in the rear side 5 may be a volume occupied bythe grooves within the panel, e.g., defined by internal walls 11 b ofthe grooves, and being limited by a horizontal plane HP provided alongthe rear side, see, e.g., FIG. 6b . The total volume TV of internalgrooves 11 may be a volume occupied by the grooves within the panel,e.g., defined by internal walls 11 b of the grooves, and being limitedby a vertical plane VP provided along the edge portions where theinternal grooves are open, see, e.g., FIG. 5 c.

Generally, a groove depth GD of the grooves 11 may be larger than 20%,such as larger than 30% or even larger than 40%, of a thickness T3 ofthe lower layer arrangement 3. In some embodiments, the groove depth GDmay be larger than 20%, such as larger than 30% or larger than 40%, of athickness T1 of the panel.

As shown in the embodiments in FIGS. 1e, 2c-2d, 5a, 5c, 6b-6c and 7a ,an innermost portion 11 a of one or several of a plurality of grooves 11may be separated from the balancing layer 4 by a distance Sa in avertical direction Z of the panel. In some embodiments, and as shown inFIG. 2a for a pair of transversely outermost grooves, but is clearlyconceivable for any, some or each of the grooves, the distance Sa may bevanishing (Sa=0). Optionally, the balancing layer 4 may be exposed frombelow when Sa=0. In some embodiments, the distance Sa may be larger than0.25 times a thickness TU of an uppermost layer 2 a, such as a wearlayer. Preferably, however, the distance is larger than 0.50 times oreven larger than 1.0 times the thickness TU of the uppermost layer 2 a.

As illustrated in, e.g., FIG. 2a , but which may be applied for anyembodiment of the first aspect, such as in FIGS. 1c-1e, 2c-2d, 5a, 5c,6a-6c and 7a , an average groove depth GA of the grooves 11 may besmaller than the thickness T3. An average-depth groove 11′ isschematically illustrated in FIG. 2 a.

Generally for the first aspect, the thickness T4 of the balancing layer4 may be at least 5%, such as at least 10% or at least 20%, of thethickness T1 of the panel. Alternatively, or additionally, a combinedthickness TL of the lower layer arrangement 3 and the balancing layer 4,may be at least 20%, such as at least 35% or at least 50%, of athickness T1 of the panel.

Moreover, the thickness T4 of the balancing layer may be larger than athickness TU of an upper layer. For example, said upper layer may be anuppermost layer 2 a, such as the wear layer. This is illustrated in,e.g., FIG. 1 e.

FIG. 5d shows in a cross-sectional side view an embodiment of a lowerlayer arrangement 3 comprising a first 3 a and a second 3 b lower layer.Any of the lower layer arrangements in FIGS. 1c-1e, 2a-2d, 5a, 5c,6a-6c, 7a-7c may be replaced with such a lower layer arrangement,preferably with grooves therein.

FIGS. 3a-3c, 4a-4c, 5b, 7d-7f, 8c and 9b illustrate embodiments of athermoplastic-based panel 1 in the form of a floor panel according tothe second aspect. The panel comprises an upper layer arrangement 2 anda balancing layer 4, which is a bottom layer 5′ of the panel. The upperlayer arrangement comprises at least one upper layer 2 a, 2 b, 2 c, 2 d.A groove arrangement 10 comprising a plurality of grooves 11 is providedin the balancing layer.

A major portion of the grooves are provided in the balancing layer 4only. At least 50% of a total volume TV of the grooves may be providedin the balancing layer only. Such a scenario is shown in thenon-limiting embodiment in FIG. 3c , which is a bottom view of the panelshown in a cross-sectional side view in FIG. 3b . Alternatively, oradditionally, a major portion of a total number of the grooves may beprovided in the balancing layer only. In FIG. 3c , for example, thereare 24 grooves provided in the balancing layer only while 9 grooves areprovided also in the upper layer arrangement 2, c.f. FIG. 3 b.

Embodiments of the upper layer arrangement 2 of the second aspect may bethe same as for the first aspect, whereby reference is made to thoseparts of the disclosure.

In some embodiments, the upper layer arrangement 2 may be laminated tothe balancing layer 4. In turn, at least some upper layers may belaminated to each other. For example, the upper layer(s) and thebalancing layer may be provided as sheets or may be provided on rollsand may be laminated to each other under heat and pressure. The sheetsmay be stacked on top of each other and, for example, may be laminatedto each other in a hot press or a multi-daylight static press. Thelayers provided on rolls may be laminated to each other in a continuousprocess. In some embodiments, the balancing layer may be coextruded withat least one upper layer, such as with all upper layers except for thewear layer and/or the print layer.

As shown in the embodiments in FIGS. 3a-3c, 4a-4c and 7d , the grooves11 may be provided in a rear side 4 a of the balancing layer and hencepreferably in a rear side 5 of the panel.

For example, the grooves may be post-formed or pre-formed as describedin relation to the first aspect. As shown in FIG. 5b , it is conceivablethat internal grooves may be provided within the balancing layer 4. Theinternal grooves may be pre-formed, such as being formed duringmanufacturing of the balancing layer and/or the panel, e.g., by (co-)extrusion. As described above, the internal grooves 10 may have wallsalong one horizontal direction and the vertical direction of the paneland may be open towards the other horizontal direction.

All of the grooves 11 may be provided in the balancing layer 4 only asshown, e.g., in the embodiments in FIGS. 3a, 4b-4c, 5b and 7 d.

Generally herein for the first, second and third aspects, the grooves 11may be provided inside all of the edge portions 1 a-1 d of the panelalong a first X and a second Y horizontal direction, see, e.g., FIGS.1c-1d and 3c . Moreover, one edge portion 16, or preferably both of theedge portions, of the grooves may be curved along a longitudinalextension of the grooves. The grooves may be open towards the rear side.

The balancing layer 4 may have a varying thickness T4 along a first Xand/or a second Y horizontal direction of the panel, for example byhaving grooves 11 provided at least partly in the balancing layer. Theembodiments in, e.g., FIGS. 3a-3c, 4a-4b and 7d illustrate a varyingthickness along the second horizontal direction Y. Optionally, thethickness may vary also along the first horizontal direction X, e.g., byhaving grooves provided inside the edge portions of the panel along thefirst horizontal direction X, see, e.g., FIG. 3 c.

As shown in, e.g., FIGS. 4c and 5b , the balancing layer 4 may have asubstantially constant thickness. For example, the balancing layer maybe (co-)extruded with at least one upper layer in the upper layerarrangement 2.

In some embodiments, and as shown in FIGS. 4a-4b , a thickness T4 of thebalancing layer is larger than a thickness TU of an upper layer of theupper layer arrangement 2. Preferably, this upper layer is an uppermostlayer 2 a of the upper layer arrangement, for example a wear layer, butother upper layers are also conceivable. As shown in FIG. 4b , thethickness T4 of the balancing layer may be larger than a thickness TU ofeach upper layer in the upper layer arrangement.

Generally for the second aspect, the thickness T4 of the balancing layer4 may be at least 20%, such as at least 35% or at least 50%, of athickness T1 of the panel.

A groove depth GD of the grooves 11 may be larger than 20%, such aslarger than 30% or even larger than 40%, of a thickness T4 of thebalancing layer 4. In some embodiments, the groove depth GD may belarger than 20%, such as larger than 30% or larger than 40%, of athickness T1 of the panel.

The embodiments in, e.g., FIGS. 3a-3b, 4a-4c, 5b and 7d show that aninnermost portion 11 a of any, some or even all of the grooves may beseparated from the upper layer arrangement 2 by a distance Sb in thevertical direction Z of the panel. The distance Sb may be larger than0.25 times a thickness TU of an uppermost layer 2 a, such as a wearlayer. Preferably, however, the distance is larger than 0.50 times oreven larger than 1.0 times the thickness TU of the uppermost layer 2 a.

In some embodiments of the first and second aspects, the groove depth GDof the grooves 11 are essentially the same, see, e.g., FIGS. 1e, 2b-2d,3a, 4a-4c, 5a-c, 6b-6c and 7d . As shown in, e.g., FIGS. 2a and 3b , itis also conceivable that the groove depth GD of at least two grooves aredifferent. The embodiments in FIGS. 2a, 3b and 7a , illustrate that thegroove depth GD of one or several grooves 11, preferably edge groovesprovided at an edge portion, such as a long edge portion 1 a, 1 b, maybe smaller than the groove depth GD of other grooves, for example agroove provided horizontally inwardly of the edge groove(s), such asalong the second horizontal direction Y.

As illustrated in, e.g., FIG. 3b , but which may be applied for anyembodiment of the second aspect, such as in FIGS. 3a, 3c, 4a-4c, 5b and7d-7f , an average groove depth GA of the grooves 11 may be smaller thanthe thickness T4. An average-depth groove 11′ is schematicallyillustrated in FIG. 3 b.

Optionally, and as illustrated in FIGS. 2b and 4b , the panel maycomprise at least one reinforcement element 13, such as a glass-fibrelayer. The at least one reinforcement element 13 may be provided in acentre portion of the panel, preferably being provided at a distance d1from the front side 12 of between 35% and 65% of a distance d2 betweenthe innermost portion 11 a and a front side 12 of the panel.

The upper layer arrangement 2 in any of the embodiments of the first andsecond aspects, for example any of those in FIGS. 1c-1e, 2a-2d, 3a-3c,4a-4c, 5a-5c, 6a -6 c, 7 a-7 f, 8 a-8 d and 9 a-9 b may comprise athermoplastic polymer, such as PVC, and, optionally, a filler, such asCaCO₃. In fact, in some embodiments each of the upper layers 2 a, 2 b, 2c, 2 d may comprise a thermoplastic polymer, such as PVC, and,optionally, a filler. The upper layer arrangement may comprise a wearlayer and/or a print layer, such as a print film. Both of these layersmay comprise a thermoplastic polymer, such as PVC. In the same manner,the lower layer arrangement 3, such as each of the at least one lowerlayer 3 a, 3 b, in any of the embodiments in FIGS. 1c-1e, 2a-2d, 5a, 5d,6a-6c, 7a-7c, 8a -8 b, 8 d and 9 a may comprise a thermoplastic polymer,such as PVC, and, optionally, a filler, such as CaCO₃. Optionally, anamount of a thermoplastic polymer in the balancing layer 4 may be higherthan an amount of a thermoplastic polymer in the upper 2 and/or lower 3layer arrangement.

Furthermore, the balancing layer 4 in any of the embodiments of thefirst and second aspects, for example any of those in FIGS. 1c-1e,2a-2d, 3a-3c, 4a-4c, 5a-5c, 6a -6 c, 7 a-7 f, 8 a-8 d and 9 a-9 b, maycomprise a thermoplastic polymer, such as PVC, and, optionally, afiller, such as CaCO₃.

The panel 1 in any of the embodiments in FIGS. 1c-1e, 2a-2d, 3a-3c,4a-4c, 5a-5c, 6a -6 c, 7 a-7 f, 8 a-8 d and 9 a-9 b may be a panel perse, e.g., configured to be laid loosely or glued to a substructure, orit may be a middle section of a panel comprising a mechanical lockingsystem 20 provided in an edge portion 1 a, 1 b, 1 c, 1 d. In the lattercase, the mechanical locking system may not be seen in said figures butmay be implicitly understood. FIGS. 6a-6c, 7a-7c, 8a-8b, 8d and 9a , onthe other hand, illustrate embodiments of floor panels 1, 1′ accordingto the first aspect and FIGS. 7d-7f, 8c and 9b illustrate embodiments offloor panels 1, 1′ according to the second aspect. The panels 1, 1′ inthese figures will be described with generic upper 2 and/or lower 3layer arrangements. An ordinarily skilled artisan will appreciate,however, that, within the scope of the present disclosure, they may beembodied as in any of the embodiments herein, for example as in any ofFIGS. 1c-1e, 2a-2d, 3a-3c, 4a-4c and 5a-5d . In particular, it isemphasized that the material composition of any of these panels mayembodied in the same manner.

FIGS. 6a-6c illustrate an embodiment of a panel 1 in a bottom view aswell as in cross-sectional side views of the panel along the long 1 a, 1b and short 1 c, 1 d edge portions. Embodiments described herein for thepanel 1 are equally possible for the adjacent panel 1′.

Any of the panels disclosed herein, such as those in any of FIGS. 1c-1e,2a-2d, 3a-3c, 4a-4c, 5a-5d, 6a -6 c, 7 a-7 f, 8 a-8 d and 9 a-9 b, maycomprise a mechanical locking system 20 in accordance with the thirdaspect for horizontally and/or vertically locking the panel 1 to anadjacent panel 1′. Such a mechanical locking system comprises acooperating surface 21 provided in an edge portion 1 a, 1 b, 1 c, 1 d ofthe panel 1 and is configured to cooperate with a cooperating surface 21of the adjacent panel 1′. The cooperating surface 21 is at leastpartially situated in the balancing layer 4 of the panel 1.

The panel 1 may be configured to be locked to the adjacent similar panel1′ on the edge portions, such as the long 1 a, 1 b and short 1 c, 1 dedge portions, by angling A and/or by a vertical displacement V withrespect to each other. FIGS. 6b, 7a-7b and 7d-7e and FIGS. 6c, 7c, 7f,8a-8d and 9a-9b show embodiments of a panel 1 configured to be locked byangling A and by a vertical displacement V, respectively. The panels 1,1′ in FIGS. 8a-8d and 9a-9b are shown around their short edge portions 1c, 1 d but alternatively, or additionally, it is equally conceivable touse any such mechanical locking system on the long edge portions 1 a, 1b of panels.

Generally, the mechanical locking system 20 of each of the panels 1, 1′may comprise at least one cooperating surface 21, preferably at leastone locking surface 22, 23 and/or at least one guiding surface 24, 25.The at least one cooperating surface 21 may be provided in an edgeportion or in opposite edge portions, such as a short 1 c, 1 d and/or along 1 a, 1 b edge portion. An ordinarily skilled artisan willappreciate that, within the scope of the present disclosure, thecooperating surface 21 may be a first cooperating surface provided in afirst edge portion, such as a long 1 a, 1 b or a short 1 c, 1 d edgeportion, and that the mechanical locking system may further comprise asecond cooperating surface 21 provided in a second opposite edgeportion, such as a short 1 c, 1 d or a long 1 a, 1 b edge portion. Thesecond cooperating surface 21 may be at least partially situated in thebalancing layer 4.

In some embodiments, the panels 1, 1′ may be formed by providing theupper layer(s) 2 a, 2 b, 2 c, 2 d and the balancing layer 4 as sheets oron rolls which then are laminated to each other under heat and pressure.Where applicable, such as in the first aspect, also the lower layer(s) 3a, 3 b may optionally be provided as sheets or on rolls and may belaminated to each other and the other layers of the panel under heat andpressure. Alternatively to the above, the balancing layer may becoextruded with at least one upper and/or lower layer. In any of thesescenarios, before forming the mechanical locking system in the panels 1,1′, the balancing layer 4 may extend into the edge portion(s) 1 a-1 d ofthe panels, see e.g. FIGS. 1c-1e, 2a-2d, 3a-3c, 4a-4c and 5a-5d . Themechanical locking system may be formed by removing material from theedge portion(s) 1 a-1 d. A portion of the balancing layer may remain inthe edge portion after the forming of the mechanical locking system, seethe embodiments in FIGS. 6a-6c, 7a-7f, 8a-8d and 9a-9b . In particular,the balancing layer may remain at substantially the same verticalposition.

The embodiments in, e.g., FIGS. 6b-6c, 7a, 7d, 8a-8d and 9b illustratepanels 1, 1′ wherein the cooperating surface 21 is a locking surface 22,23 configured to engage with a locking surface 23, 22 of the adjacentpanel 1′/panel 1 in a locked state. As shown, the locking surfaces 22,23 may be at least partially situated in the balancing layer 4 of therespective panel 1, 1′. Generally, the locking surfaces 22, 23 may bevertical and/or horizontal locking surfaces 22, 23. In FIG. 7a , thelocking surface 22 includes an upward-facing horizontal recessed portionof the cooperating surface 21. In FIG. 7a , this lowermost upward-facinghorizontal recessed portion is a surface of the balancing layer 4.

The embodiments in, e.g., FIGS. 7b-7c, 7e-7f and 9a-9b illustrate panels1, 1′ wherein the cooperating surface 21 is a guiding surface 24, 25configured to guide the adjacent panel 1′/panel 1 during locking. Theguiding may be implemented by a guiding surface 24, 25 cooperating orengaging with a cooperating surface 21, such as guiding surface 25, 24,of the adjacent panel during locking. As shown, the guiding surface(s)24, 25 may be at least partially situated in the balancing layer 4 ofthe respective panel 1, 1′. Generally, the guiding surfaces 24, 25 mayguide the adjacent panel vertically and/or horizontally.

As shown in e.g. FIGS. 6b-c , the mechanical locking system 20 of thepanel 1, such as on the long 1 a, 1 b and/or short 1 c, 1 d edgeportions, may comprise a locking element 8, 8′ provided on a strip 6, 6′configured to engage with a locking groove 14, 14′ of the adjacent panel1′ for horizontal locking. The strip 6, 6′ may extend horizontallyinwardly of, and may comprise a portion which is thinner than, thelocking element 8, 8′. The balancing layer 4 may at least partiallyextend through the locking element 8, 8′ and/or through the lockinggroove 14, 14′. Moreover, the cooperating surface 21 may be situated onthe locking element 8, 8′ and/or in the locking groove 14, 14′. In someembodiments, and as shown in, e.g., FIGS. 6b-6c, 7c-7f, 8a-8d and 9a-9b, an uppermost surface 8 a, 8 a′ of the locking element may comprise aportion of the balancing layer and a cooperating surface 21, such as alocking surface 22 and/or a guiding surface 24, may be provided in theuppermost surface 8 a, 8 a′.

The balancing layer 4 may at least partially extend along the strip 6,6′, such as along an upper portion of the strip. For example, thebalancing layer 4 may extend along a part of, or the entire, upwardfacing surface(s) of the strip 6, 6′. As shown in, e.g., FIGS. 7a-7b,7d-7f, 8a, 8c-8d and 9a-9b , an uppermost surface 6 a, 6 a′ of the stripmay comprise a portion of the balancing layer. A cooperating surface 21,such as a locking surface 22 and/or a guiding surface 24, may beprovided in the uppermost surface 6 a, 6 a′.

As shown in, e.g., FIGS. 7f and 8a , a transitional surface 26transitioning from the uppermost surface 6 a′ of the strip 6′ to thelocking element 8′, such as an inner wall 8 b′ of the locking element,may comprise a portion of the balancing layer 4. The uppermost surface 6a′ may be provided horizontally inwardly of the locking element 8′. Thisembodiment may be particularly advantageous on a short edge portion 1 dwhere particularly high stresses are conceivable.

Furthermore, the mechanical locking system 20 of the panel 1, such as onthe long 1 a, 1 b and/or short 1 c, 1 d edge portions, may comprise atongue portion 9, 9′ configured to engage with a tongue groove 7, 7′ ofthe adjacent panel 1′ for vertical locking. The balancing layer 4 may atleast partially extend through the tongue portion 9, such as through alower portion of the tongue portion. As illustrated in, e.g., FIGS.6b-6c, 7a-7f, 8a-8d and 9a-9b , a cooperating surface 21, such as alocking surface 22, 23 and/or a guiding surface 24, 25, may be situatedon the tongue portion 9, 9′. A lowermost surface 9 a, 9 a′ of the tongueportion may comprise a portion of the balancing layer and thecooperating surface 21 may be provided in the lowermost surface 9 a, 9a′, see, e.g., FIGS. 7a-7b, 7d-7f, 8a, 8c-8d and 9a -9 b.

As shown in, e.g., FIG. 6b , the tongue portion 9, preferably providedin a long edge portion 1 a, may comprise a tongue 18 that is integrallyformed with the panel. Moreover, as shown in, e.g., FIG. 6c , the tongueportion 9′, preferably provided in a short edge portion 1 d, maycomprise a separate, and preferably flexible, tongue 18′ that isconfigured to be provided in a displacement groove 19 provided at anedge portion, such as the short edge portion 1 d, of the panel. Anon-limiting embodiment of a tongue 18′ is illustrated in FIG. 6c in across-sectional top view. This so-called bristle tongue is preferablyformed in one-piece and comprises flexible protrusions 28.

The cooperating surface 21, such as a locking surface and/or guidingsurface, of the adjacent panel 1′ may be a general cooperating surfaceprovided at the edge portion. Optionally, however, it may be at leastpartially situated in the balancing layer 4 of the adjacent panel 1′. Ina first example, and as shown in, e.g., FIGS. 8a-8d , but which isgenerally applicable, e.g., for the embodiments in FIGS. 6b-6c and 7a-7f, in a locked state, a portion of a vertical and/or a horizontal lockingsurface 22 of panel 1 comprising the balancing layer 4 may be configuredto engage with a portion of a vertical and/or a horizontal lockingsurface 23 of panel 1′ comprising the balancing layer 4. In a secondgeneral example, and as shown in, e.g., FIGS. 7b-7c, 7e-7f and 9a-9b ,during locking, a portion of a vertical and/or a horizontal guidingsurface 24 of panel 1 comprising the balancing layer 4 may be configuredto cooperate with a portion of a vertical and/or a horizontal guidingsurface 25 of panel 1′ comprising the balancing layer 4. A third generalexample includes all portion configurations of the first and secondexamples.

It is emphasized that the roles of the panel 1 and the adjacent panel 1′described herein may be interchanged.

In a first example, and as illustrated in, e.g., FIGS. 7b-7c, 7e-7f and9a-9b , the guiding surface 25 of the panel 1′ may be provided in anedge portion 1 a, 1 c, may be at least partially situated in thebalancing layer 4 of the panel 1′, and may be configured to cooperatewith a cooperating surface 21 of the panel 1 during locking. Embodimentsand examples of the guiding surface 25 of the panel 1′ have beendescribed above in relation to these figures. As shown in FIGS. 7b, 7eand 9a-9b , such a cooperating surface 21 may be provided on theuppermost surface 6 a of the strip 6 and/or on the locking element 8. Asshown in FIGS. 9a-9b , such a cooperating surface 21 may also beprovided in a wall 27 in the upper edge of the panel 1, optionally beingprovided along a vertical plane VP defined by juxtaposed upper edges ofthe panels 1, 1′. Moreover, as shown in FIGS. 7c and 7f , such acooperating surface 21 may be provided in a wall 27 in the upper edge ofthe panel 1 provided along said vertical plane VP and/or on theseparate, and preferably flexible, tongue 18′.

In a second example, and as illustrated in, e.g., FIGS. 8a-8d , thelocking surface 23 of the panel 1′ may be provided in an edge portion 1c, may be at least partially situated in the balancing layer 4 of thepanel 1′, and may be configured to engage with a locking surface 22 ofthe panel 1 in a locked state of the panels 1, 1′. As shown in FIGS.8a-8d , such a locking surface 22 may be provided on the uppermostsurface 6 a of the strip 6 and/or on the locking element 8, such as inan uppermost surface 8 a, an inner wall 8 b and/or an outer wall 8 cthereof.

An ordinarily skilled artisan will appreciate that, within the scope ofthe present disclosure, in some embodiments, the mechanical lockingsystem 20 comprises a cooperating surface 21 at least partially situatedin the balancing layer 4 and, in addition, comprises a cooperatingsurface 21 only provided in the upper 2 and/or lower 3 layerarrangement.

It is yet again stressed that the groove arrangement 10 is optional withrespect to the third aspect. Indeed, the embodiments in, e.g., FIGS.8a-8d and 9a-9b are illustrated without any grooves 11 therein, eventhough grooves, such as those shown in any of the embodiments in FIGS.6a-6c, 7a and 7d , clearly are not excluded. It is also noted that inany embodiment herein, the grooves may be provided between themechanical locking system 20 provided at a pair of opposite edgeportions, such as short edge portions 1 c, 1 d. As shown in, e.g., FIG.6c , a groove length GL may be smaller than a distance DM between themechanical locking system 20 at the pair of opposite edge portions, suchas between inner portions thereof.

In some embodiments, and as illustrated in FIG. 9a as well as in FIGS.8a-8c , the groove arrangement 10 may comprise a calibrating groove 15for facilitating locking of the panels, such as when the panels havediverging thicknesses or when no underlay element, such as a foam, isused. The calibrating groove 15 may be provided at the edge portion ofthe adjacent panel 1′, preferably in a rear side 5 thereof. Moreover,the calibrating groove 15 may be provided adjacent, such as directlyadjacent, to the locking groove 14.

TABLE 1 Embodiments of layer combinations in the first aspect A1 A2 A3A4 A5 Upper layer L1 U1 L1 U1 L1 Balancing layer L3 L3 L3 U2 U2 Lowerlayer L1 U1 E1 U1 E1

TABLE 2 Embodiments of layer combinations in the first aspect B1 B2 B3B4 B5 First upper layer L2 U2 L2 L2 U2 Second upper layer L1 U1 U1 L1 U1Balancing layer L3 U2 L3 L3 U2 Lower layer Ll U1 U1 E1 E1

TABLE 3 Embodiments of layer combinations in the second aspect C1 C2 C3C4 Upper layer L1 U1 L1 U1 Balancing layer L3 L3 U2 U2

TABLE 4 Embodiments of layer combinations in the second aspect D1 D2 D3D4 D5 D6 First upper layer L2 L1 L1 L1 U1 U2 Second upper layer L1 E1 U1E1 E1 U1 Balancing layer L3 L3 L3 U2 U2 U2

TABLE 5 Examples of material compositions in the first and secondaspects PVC CaCO₃ Plasticizer Additives Foaming agent (wt %) (wt %) (wt%) (wt %) (wt %) L1 10-35 60-90  2-20 0.5-10.0 0-3 L2 20-50 40-80  2-200.5-10.0 0-3 L3 30-70 20-70  2-20 0.5-10.0 0-3 U1 10-40 60-85 0-50.5-10.0 0-3 U2 20-50 40-70 0-5 0.5-10.0 0-3 E1 30-60 40-60 0-5 0.5-10.00.1-5.0

Tables 1 and 2 illustrate non-limiting embodiments, respectively, oflayer combinations A1, . . . , A5 and B1, . . . , B5 of the first aspectthat are conceivable for any of the panels in, e.g., FIGS. 1c-1e, 2a-2d,5a, 5c, 6a-6c, 7a-7c, 8a -8 b, 8 d and 9 a. Moreover, Tables 3 and 4illustrate non-limiting embodiments, respectively, of layer combinationsC1, . . . , C4 and D1, . . . , D6 of the second aspect that areconceivable for any of the panels in, e.g., FIGS. 3a-3c, 4a-4c, 5b,7d-7f, 8c and 9b . An ordinarily skilled artisan will appreciate that,within the scope of the present disclosure, a panel comprising any ofthe layer combinations in Tables 1-4 additionally may comprise a wearlayer and/or a print layer. Additionally, a coating, such as an UVcoating, may be provided on the upper layer arrangement. For the layercombinations B1, . . . , B5 and D1, . . . , D6, the first upper layermay be provided above the second upper layer. Generally, each of theupper layer(s), the lower layer and balancing layer may comprise athermoplastic polymer, such as PVC. Preferably, each of said layerscomprises a filler, such as CaCO₃. Moreover, each layer may comprise aplasticizer and/or additives, such as a stabilizer, an impact modifier,a pigment, or a lubricant, and, optionally, a foaming agent.

Non-limiting examples of material compositions L1-L3, U1, U2 and E1 ofupper layers, lower layers and the balancing layer—specified in weightpercentages (wt %)—are shown in Table 5. These material compositions maybe applied to any of the layer combinations in Tables 1-4.

In some embodiments, the upper layer(s) and the balancing layer maycomprise different material compositions, cf. A1-A5, B1, B3-B4, C1-C4and D1-D5. Moreover, in some embodiments, an upper layer and thebalancing layer may comprise a substantially similar materialcomposition, cf. B2, B5 and D6. In some embodiments of the first aspect,the upper layer(s) and the lower layer, may comprise different materialcompositions, cf. A3, A5 and B4-B5. In some embodiments, however, anupper layer and a lower layer may comprise a substantially similarmaterial composition, cf. A1, A2, A4 and B1-B3. In any of theseembodiments, the thicknesses of the layers having a substantiallysimilar material composition may be different.

In accordance with a fourth aspect of the disclosure, a panel assemblycomprises a building panel and an adjacent building panel, wherein thebuilding panel and/or the adjacent building panel may be embodied as thebuilding panel according to any of the embodiments and examples of thefirst, second and third aspects. Examples of a panel assembly accordingto the fourth aspect are shown being assembled in FIGS. 7b, 7c, 7e, 7f,9a and 9b . Other examples of a panel assembly according to the fourthaspect in an assembled state are shown in FIGS. 8a -8 d.

Aspects of the disclosure have mainly been described above withreference to a few embodiments. However, as would be readily appreciatedby a person skilled in the art, other embodiments than the onesdisclosed above are equally possible within the scope of the disclosure,as defined by the appended patent claims and items in an embodimentsection below. For instance, in any embodiment herein, and asschematically illustrated in FIG. 2d , a separately formed underlayelement 17, such as a foam or cork, may at least partially cover therear side 5 of the panel, which may be provided in the lower layerarrangement 3 (first aspect) or in the balancing layer 4 (secondaspect).

Examples

The following examples further describe and demonstrate embodimentswithin the scope of the present disclosure. The examples are givensolely for the purpose of illustration and are not to be construed aslimitations of the present disclosure, as many variations thereof arepossible without departing from the spirit and scope of the disclosure.

To test the curling effect of the panels in accordance with the firstaspect, the following measurements were conducted utilizing an IndicatorMethod on each of a set of samples S1, S2 and S3, each sample havinghorizontal dimensions 160×160 mm. These samples are represented in FIGS.10a-10c as photos together with a ruler indicating a millimetre scale.FIG. 10a shows a photo of a sample S1 (reference) produced with groovesfully penetrating a balancing layer provided as a bottom layer, whileFIGS. 10b-10c show photos of samples S2, S3 produced in accordance withthe first aspect, in the case when the grooves were provided in thelower layer only.

The compositions COM1, COM2 and WL0 were used in the samples. Specifiedin weight percentages, COM1 comprised 16.92% PVC (Norvinyl™ S5745),76.14% CaCO₃ (Greenafiller™ 0-100), 0.34% stabilizer (Baerostab™ CT 1228R), 0.08% lubricant (Baerolub™ PA Special), 6.43% plasticizer (Eastman™168) and 0.08% black pigments. Moreover, COM2 comprised 37.04% PVC(Norvinyl™ S5745), 50.00% CaCO₃ (Greenafiller™ 0-100), 0.74% stabilizer(Baerostab™ CT 1228 R), 0.19% lubricant (Baerolub™ PA Special), 11.85%plasticizer (Eastman™ 168) and 0.19% red pigments. WL0 comprisedadditives and a plasticizer and 75 wt % of PVC. The thicknesses of thelayers of the samples, the total thickness of the samples and the groovedepths GD are specified in millimetres in Table 6 and the materialcompositions of the layered structures are specified in Table 7. Each ofthe samples S1, S2 and S3 comprised a wear layer comprising additivesand a plasticizer and 75 wt % of PVC and, additionally, a print layercomprising a PVC and white pigments and having a thickness of 0.04 mm.

TABLE 6 Sample data Wear Upper Balancing Lower Total Groove Layer LayerLayer Layer Thickness Depths Sample (mm) (mm) (mm) (mm) (mm) (mm) S10.54 3.60 0.93 — 5.1 1.90-2.01 S2 0.56 1.92 0.92 1.99 5.4 1.95-2.02 S30.54 1.93 0.99 1.89 5.4 1.91-1.98 S4 0.56 3.73 1.31 — 5.66 2.03 S5 0.571.85 1.20 2.01 5.69 1.99 S6 0.52 4.00 0.98 — 5.56 1.71-1.78 S7 0.52 3.012.00 — 5.66 1.74-1.75 S8 0.55 1.94 3.38 — 5.93 1.76-1.82

Measurements were conducted for each of the samples S1, S2 and S3 byusing an indicator device 30 schematically illustrated in a side view inFIG. 9c . The indicator device comprised a pair of abutment portions 31fixedly arranged on opposite sides 33 of a bar 32 at the same level. Adisplaceable indicator 34 arranged between the abutment portions 31 wasconfigured to measure a deviation Δz of the displaceable indicator 34with respect to the abutment portions 31 along a direction F beingparallel with the displacement direction of the displaceable indicator34.

FIG. 9d shows a cross-sectional top view along the section E-E in FIG.9c . FIG. 9e shows the same cross-sectional top view as in FIG. 9c , butwith the indicator device 30 being rotated by 90 degrees in the X-Yplane. For each sample a measurement was made along centre lines CX andCY of the sample which were parallel with the first X and second Yhorizontal direction, respectively.

TABLE 7 Material compositions and test results of the samples UpperBalancing Lower Δz₁₂ (X) Δz₁₂ (Y) Sample Layer Layer Layer (mm) (mm) S1COM1 COM2 — −0.40 −0.42 S2 COM1 COM2 COM1 −0.24 −0.09 S3 COM1 WL0 COM1−0.14 −0.02

More specifically, the abutment portions 31 abutted the sample along thecentre line CX at a distance of 5 mm from the edges of the sample andthe displaceable indicator 34 engaged with a centre point C0 of thesample, see FIG. 9d . Thereby, a vertical deviation Δz₁(X) was deducedat a temperature of 22° C. Also a vertical deviation Δz₁(Y) along thecentre line CY was deduced at the same temperature using a similarprocedure, see FIG. 9 e.

The sample was then heated to a temperature of 80° C. and was maintainedat that temperature for six hours. Thereafter, the sample wasacclimatized to a temperature of 22° C. for 24 hours. Afteracclimatization of the sample the vertical deviations Δz(X) and Δz(Y)were remeasured using the same approach as described above for obtainingthe values Δz₂(X) and Δz₂(Y). The measured differencesΔz₁₂(X)=Δz₁(X)-Δz₂(X) and Δz₁₂(Y)=Δz₁(Y)-Δz₂(Y) are summarized in Table7. It may be seen that, as compared to the sample S1, the curling effectsignificantly decreased along the first X and second Y horizontaldirections for S2 and S3 as a result of displacing the balancing layerin accordance with the first aspect.

The curling effect was also tested on a sample S5 in accordance with thefirst aspect and samples S7 and S8 in accordance with the second aspect.FIG. 11a shows a photo of the sample S5 produced in accordance with thefirst aspect and FIGS. 11c-11d show photos of the samples S7 and S8produced in accordance with the second aspect. The grooves in S5 (S7-58)were provided in the lower layer only (in the balancing layer only). Tosee the improvement, the sample S5 (S7 or S8) was compared to referencesample S4 (S6) produced with grooves fully penetrating a balancing layerprovided as a bottom layer. Photos of S4 and S6 are shown in FIG. 10dand FIG. 11b , respectively.

The curling effect was tested using the standard ISO 23999:2018, withthe modification that each sample S4-S8 had a size of 160×160 mm(instead of 229×229 mm). The compositions COM1 (specified above), COM3and COM4 were used in the samples. Specified in weight percentages, COM3comprised 56.34% PVC (Norvinyl™ S5745), 28.17% CaCO₃ (Greenafiller™0-100), 1.13% stabilizer (Baerostab™ CT 1228 R), 0.28% lubricant(Baerolub™ PA Special) and 14.08% plasticizer (Eastman™ 168) and COM4comprised 37.11% PVC (Norvinyl™ S5745), 50.09% CaCO₃ (Greenafiller™0-100), 0.74% stabilizer (Baerostab™ CT 1228 R), 0.19% lubricant(Baerolub™ PA Special) and 11.87% plasticizer (Eastman™ 168).

The thicknesses and the groove depths GD of S4-S8 specified in mm aresummarized in Table 6 and the material compositions are specified inTable 8. Each of the samples S4-S8 comprised a PVC wear layer and aprint film comprising PVC having a thickness of about 0.60 mm and 0.06mm, respectively. The measured differences Δz₁₂(X) and Δz₁₂(Y) using theIndicator Method as well as the mean value for curling using ISO23999:2018 are summarized in Table 8 in mm. It may be seen that, ascompared to the sample S4, the curling effect of S5 (first aspect)decreased using both tests. In particular, Δz₁₂(Y) significantlydecreased. Moreover, as compared to the sample S6, the curling effect ofS7 and S8 (second aspect) decreased significantly using both tests.

TABLE 8 Material compositions and test results of the samples UpperBalancing Lower Δz₁₂(X) Δz₁₂(Y) ISO 23999 Sample Layer Layer Layer (mm)(mm) (mm) S4 COM1 COM3 — 0.26 0.70 1.11 S5 COM1 COM3 COM1 0.25 0.13 0.44S6 COM1 COM4 — 0.47 0.72 0.99 S7 COM1 COM4 — 0.29 0.46 0.46 S8 COM1 COM4— 0.14 0.13 0.049

TABLE 9 Material compositions and sample data Sample UL1 UL2 BL LL (mm)GD Q1 COM4; 1.0 COM6; 3.0 COM4; 1.0 — 1.7 Q2 COM4; 1.0 COM6; 1.0 COM4;1.0 COM6; 2.0 1.6 Q3 COM5; 1.0 COM6; 3.0 COM5; 1.0 — 2.0 Q4 COM5; 1.0COM6; 1.0 COM5; 1.0 COM6; 2.0 2.0

A pair of samples Q2 and Q4 in accordance with the first aspect weretested with respect to residual indentation by means of the standardASTM F1914-18 (product specification ASTM F1700). The resilient sampleQ2 and the rigid sample Q4 were compared to reference samples Q1 and Q3,respectively, which had a similar layer composition, but were notprovided with a lower layer LL present in Q2 and Q4. Each sample Q1-Q4had two upper layers UL1, UL2, a balancing layer BL and horizontaldimensions 50×50 mm. The grooves in Q2 and Q4 were provided in the lowerlayer only and the grooves in Q1 and Q3 were fully penetrating thebalancing layer BL provided as a bottom layer. An IXPE foam having athickness of 1.5 mm was used as an underlay, thereby covering thegrooves. FIGS. 12a-12d show photos of the samples Q1-Q4, respectively,during the tests.

The compositions COM4 (specified above), COM5 and COM6 were used in thesamples. Specified in weight percentages, COM5 comprised 37.59% PVC(Norvinyl™ S6261), 56.38% CaCO₃ (Greenafiller™ 0-100), 0.21% pigments(Printex™ Carbon Black), 3.76% stabilizer (Baerostab™ CT 1229 P), 0.28%processing aid and lubricant (Baerocid™ SMS 1A), 0.28% lubricant(Baerolub™ PA 200), 1.13% impact modifier (Addstrength™ CPE-3516) and0.38% impact modifier (Kane Ace™ B580) and COM6 comprised 27.32% PVC(Norvinyl™ S6261), 68.30% CaCO₃ (Greenafiller™ 0-100), 0.15% pigments(Printex™ Carbon Black), 2.73% stabilizer (Baerostab™ CT 1229 P), 0.20%processing aid and lubricant (Baerocid™ SMS 1A), 0.20% lubricant(Baerolub™ PA 200), 0.82% impact modifier (Addstrength™ CPE-3516) and0.27% impact modifier (Kane Ace™ B580).

The material compositions, the layer thicknesses (in mm) and the groovedepths GD (in mm) of Q1-Q4 are specified in Table 9. Both of the samplesQ1 and Q3 were broken in the test, while the samples Q2 and Q4 resultedin a residual indentation of 2.896% and 1.390%, respectively. Hence, itmay be concluded that the sample properties concerning residualindentation was significantly improved when the balancing layer wassandwiched between the upper and lower layer arrangements.

It is noted that similar results may be deduced for the second aspect.Indeed, by analogy, an ordinarily skilled artisan would expect a moreintact bottom layer (lower layer or balancing layer) comprising groovesto perform better with regards to residual indentation.

Illustrative Embodiments

Further aspects of the disclosure are provided below. Embodiments,examples etc. of these aspects are largely analogous to the embodiments,examples, etc. as described above, whereby reference is made to theabove for a detailed description.

Item 1. A thermoplastic-based building panel (1), such as a floor panel,comprising:

-   -   an upper layer arrangement (2) comprising at least one upper        layer (2 a, 2 b, 2 c),    -   a lower layer arrangement (3) comprising at least one lower        layer (3 a, 3 b), and    -   a balancing layer (4) being provided between said lower layer        arrangement and said upper layer arrangement,        wherein the building panel further comprises a groove        arrangement (10) comprising at least one groove (11), preferably        a plurality of grooves.

Item 2. The building panel according to item 1, wherein the groovearrangement is provided in the lower layer arrangement (3).

Item 3. The building panel according to item 1 or 2, wherein the atleast one groove (11) is provided in a rear side (5) of the lower layerarrangement (3), preferably in a bottom layer (5′) thereof.

Item 4. The building panel according to any of the preceding items,wherein a groove depth (GD), preferably a maximal groove depth, of theat least one groove is larger than 20%, such as larger than 30% orlarger than 40%, of a thickness (T3) of the lower layer arrangement (3)and/or of a thickness (T1) of the building panel.

Item 5. The building panel according to any of the preceding items,wherein a major portion of said grooves are provided entirely below thebalancing layer.

Item 6. The building panel according to any of the preceding items,comprising a plurality of grooves in the lower layer arrangement,wherein an innermost portion (11 a) of at least one groove is separatedfrom the balancing layer (4) by a distance (Sa) in the verticaldirection of the building panel.

Item 7. The building panel according to any of the preceding items,wherein a combined thickness (TL), such as a maximal combined thickness,of the lower layer arrangement (3) and the balancing layer (4), is atleast 20%, such as at least 35% or at least 50%, of a thickness (T1) ofthe building panel.

Item 8. The building panel according to any of the preceding items,wherein a thickness (T4), such as a maximal thickness, of the balancinglayer (4) is at least 5%, such as at least 10% or at least 20%, of athickness (T1) of the building panel.

Item 9. The building panel according to any of the preceding items,wherein a thickness (T4), such as a maximal thickness, of the balancinglayer (4) is larger than a thickness (TU) of an upper layer of the upperlayer arrangement, said upper layer preferably being an uppermost layer(2 a) of the upper layer arrangement.

Item 10. A thermoplastic-based building panel (1), such as a floorpanel, comprising:

-   -   an upper layer arrangement (2) comprising at least one upper        layer (2 a, 2 b, 2 c), and    -   a balancing layer (4) being a bottom layer (5′) of the building        panel,        wherein the building panel further comprises a groove        arrangement (10) comprising a plurality of grooves (11), a major        portion of said grooves being provided in the balancing layer        only.

Item 11. The building panel according to item 10, wherein all of saidgrooves are provided in the balancing layer only.

Item 12. The building panel according to item 10 or 11, wherein saidgrooves are provided in a rear side (4 a) of the balancing layer.

Item 13. The building panel according to any of the preceding items10-12, wherein said major portion comprises a major portion of a totalvolume (TV) of the grooves and/or a major portion of a total number ofgrooves.

Item 14. The building panel according to any of the preceding items10-13, wherein a thickness (T4), such as a maximal thickness, of thebalancing layer is larger than a thickness (TU) of an upper layer of theupper layer arrangement, said upper layer preferably being an uppermostlayer (2 a) of the upper layer arrangement.

Item 15. The building panel according to any of the preceding items10-14, wherein a thickness (T4), such as a maximal thickness, of thebalancing layer (4) is at least 20%, such as at least 35% or at least50%, of a thickness (T1) of the building panel.

Item 16. The building panel according to any of the preceding items10-15, comprising a plurality of grooves in the balancing layer, whereinan innermost portion (11 a) of at least one groove is separated from theupper layer arrangement by a distance (Sb) in the vertical direction ofthe building panel.

Item 17. The building panel according to any of the preceding items10-16, wherein a groove depth (GD) of the groove(s) is larger than 20%,such as larger than 30% or larger than 40%, of a thickness (T4) of thebalancing layer and/or of a thickness (T1) of the building panel, suchas floor panel.

Item 18. The building panel according to any of the preceding items1-17, comprising a plurality of grooves, wherein a groove depth (GD),preferably a maximal groove depth, of at least two grooves aredifferent.

Item 19. The building panel according to any of the preceding items1-18, wherein the balancing layer is a continuous layer.

Item 20. The building panel according to any of the preceding items1-19, comprising at least one reinforcement element, such as aglass-fibre layer.

Item 21. The building panel according to any of the preceding items1-20, further comprising a mechanical locking system (20) in an edgeportion (1 a, 1 b; 1 c, 1 d) for horizontally and/or vertically lockingthe building panel to an adjacent building panel.

Item 22. The building panel according to any of the preceding items1-21, further comprising a mechanical locking system (20) according toitem 23 or any of the items 26-38.

Item 23. A thermoplastic-based building panel (1; 1′), such as a floorpanel, comprising:

-   -   an upper layer arrangement (2) and/or a lower layer arrangement        (3),    -   a balancing layer (4) comprising a thermoplastic polymer, and    -   a mechanical locking system (20) for horizontally and/or        vertically locking the building panel (1; 1′) to an adjacent        building panel (1′; 1), the mechanical locking system comprising        a cooperating surface (21) provided in an edge portion (1 a, 1        b; 1 c, 1 d) of the building panel (1; 1′) and being configured        to cooperate with a cooperating surface (21) of the adjacent        building panel (1′; 1),        wherein the cooperating surface (21) of the mechanical locking        system (20) is at least partially situated in the balancing        layer.

Item 24. The building panel according to item 23, wherein the balancinglayer is provided between said lower layer arrangement (3) and saidupper layer arrangement (2).

Item 25. The building panel according to item 23, wherein the balancinglayer is a bottom layer (5′) of the building panel.

Item 26. The building panel according to any of the preceding items23-25, wherein the balancing layer at least partially extends through alocking element (8; 8′) provided on a strip (6; 6′) and/or through alocking groove (14; 14′) the locking element being configured to engagewith the locking groove of said adjacent building panel (1′) forhorizontal locking.

Item 27. The building panel according to item 26, wherein thecooperating surface is situated on the locking element (8; 8′) and/or inthe locking groove (14; 14′).

Item 28. The building panel according to item 26 or 27, wherein anuppermost surface (8 a; 8 a′) of the locking element comprises a portionof the balancing layer, said cooperating surface preferably beingprovided in the uppermost surface.

Item 29. The building panel according to any of the preceding items23-28, wherein the balancing layer at least partially extends along astrip (6; 6′), such as along an upper portion of the strip.

Item 30. The building panel according to item 29, wherein an uppermostsurface (6 a; 6 a′) of the strip comprises a portion of the balancinglayer, said cooperating surface (21) preferably being provided in theuppermost surface (6 a; 6 a′).

Item 31. The building panel according to any of the preceding items23-30, wherein the balancing layer at least partially extends through atongue portion (9; 9′), such as through a lower portion of the tongueportion, the tongue portion being configured to engage with a tonguegroove (7; 7′) of the adjacent building panel for vertical locking.

Item 32. The building panel according to item 31, wherein thecooperating surface is situated on the tongue portion (9; 9′).

Item 33. The building panel according to item 31 or 32, wherein alowermost surface (9 a; 9 a′) of the tongue portion comprises a portionof the balancing layer, said cooperating surface preferably beingprovided in the lowermost surface.

Item 34. The building panel according to any of the preceding items23-33, wherein the cooperating surface (21) is a first cooperatingsurface provided in a first edge portion (1 a, 1 b; 1 c, 1 d) of thebuilding panel and wherein the mechanical locking system furthercomprises a second cooperating surface provided in a second edge portion(1 c, 1 d; 1 a, 1 b) of the building panel, the first and second edgeportions preferably being oppositely arranged on the building panel,wherein the second cooperating surface is at least partially situated inthe balancing layer (4).

Item 35. The building panel according to any of the preceding items23-34, wherein the cooperating surface (21) is a locking surface (22;23) configured to engage with a locking surface (23; 22) of the adjacentbuilding panel in a locked state of the building panel and the adjacentbuilding panel.

Item 36. The building panel according to any of the preceding items23-35, wherein the cooperating surface (21) is a guiding surface (24;25) configured to guide the adjacent building panel during locking ofthe building panel to the adjacent building panel, such as bycooperating or engaging with a cooperating surface (21), such as aguiding surface (25; 24), of the adjacent building panel during locking.

Item 37. The building panel according to any of the preceding items23-36, wherein the building panel further comprises a groove arrangement(10) comprising at least one groove (11), preferably a plurality ofgrooves.

Item 38. The building panel according to any of the preceding items23-37, wherein the building panel and the adjacent building panel areconfigured to be locked to each other by angling and/or a relativevertical displacement of the building panels towards each other.

Item 39. The building panel according to any of the preceding items1-38, wherein the upper layer arrangement (2), such as each of said atleast one upper layer, comprises a thermoplastic polymer and,optionally, a filler.

Item 40. The building panel according to any of the preceding items1-39, wherein the upper layer arrangement comprises a wear layer (2 a)and/or a print layer (2 b), such as a print film.

Item 41. The building panel according to any of the preceding items1-40, wherein the balancing layer (4) comprises a thermoplastic polymerand, optionally, a filler.

Item 42. The building panel according to any of the preceding items1-41, wherein the lower layer arrangement (3), such as each of said atleast one lower layer, comprises a thermoplastic polymer and,optionally, a filler.

Item 43. The building panel according to any of the preceding items1-42, wherein an amount of a thermoplastic polymer in the balancinglayer is higher than an amount of a thermoplastic polymer in the upperand/or lower layer arrangement.

Item 44. The building panel according to any of the preceding items1-43, wherein at least one upper and/or lower layer of said buildingpanel is extruded, such as coextruded.

Item 45. The building panel according to any of the preceding items 1-22or 37-44, wherein the groove arrangement (10) is post-formed afterforming the panel (1) per se, preferably by removing material from abottom layer (5′) of the panel.

Item 46. The building panel according to any of the preceding items 1-9or 37-45, wherein an average groove depth (GA) of a plurality of grooves(11) is smaller than a thickness (T3) of the lower layer arrangement.

Item 47. The building panel according to any of the preceding items10-22 or 37-45, wherein an average groove depth (GA) of a plurality ofgrooves (11) is smaller than a thickness (T4) of the balancing layer.

Item 48. The building panel according to any of the preceding claims,comprising a groove arrangement (10) comprising at least one groove(11), wherein the at least one groove (11) includes at least one openingat a bottom-facing surface of the building panel (1).

Item 49. The building panel according to any of the preceding claims,comprising a groove arrangement (10) comprising at least one groove(11), wherein the at least one groove (11) is bounded by a panel portionlocated below the at least one groove (11).

Item 50. The building panel according to item 35, wherein the lockingsurface (22) includes an upward-facing horizontal recessed portion ofthe cooperating surface (21).

Item 51. The building panel according to item 50, wherein theupward-facing horizontal recessed portion is a surface of the balancinglayer (4).

Item 52. Panel assembly comprising a building panel (1) and an adjacentbuilding panel (1′), wherein the building panel and/or the adjacentbuilding panel is embodied as the building panel according to any of thepreceding items 1-51.

1. A thermoplastic-based building panel having a reduced weight and/or areduced material content, comprising: an upper layer arrangementcomprising a thermoplastic polymer and, optionally, a filler, the upperlayer arrangement comprising at least one upper layer, a lower layerarrangement comprising a thermoplastic polymer and, optionally, afiller, the lower layer arrangement comprising at least one lower layer,and a balancing layer comprising a thermoplastic polymer and,optionally, a filler, the balancing layer being provided between saidlower layer arrangement and said upper layer arrangement, wherein thebuilding panel further comprises a groove arrangement comprising atleast one groove, preferably a plurality of grooves, a groove depth ofthe at least one groove being larger than 20% of a thickness of thebuilding panel, wherein the groove arrangement is provided in the lowerlayer arrangement, and wherein the groove arrangement is post-formedafter forming the panel per se by removing material from a bottom layerof the building panel.
 2. The building panel according to claim 1,wherein the at least one groove is provided in a rear side of the lowerlayer arrangement, preferably in a bottom layer thereof.
 3. The buildingpanel according to claim 1, wherein a groove depth of the at least onegroove is larger than 20% of a thickness of the lower layer arrangement.4. The building panel according to claim 1, wherein a groove depth ofthe at least one groove is larger than 30% of a thickness of thebuilding panel.
 5. The building panel according to claim 1, wherein amajor portion of said grooves are provided entirely below the balancinglayer.
 6. The building panel according to claim 1, comprising aplurality of grooves in the lower layer arrangement, wherein aninnermost portion of at least one groove is separated from the balancinglayer by a distance in the vertical direction of the building panel. 7.The building panel according to claim 1, wherein a thickness of thebalancing layer is at least 10% of a thickness of the building panel. 8.The building panel according to claim 1, wherein a thickness of thebalancing layer is larger than a thickness of an upper layer of theupper layer arrangement, said upper layer preferably being an uppermostlayer of the upper layer arrangement.
 9. The building panel according toclaim 1, wherein the balancing layer is a continuous layer.
 10. Thebuilding panel according to claim 1, wherein an amount of athermoplastic polymer in the balancing layer is higher than an amount ofa thermoplastic polymer in the upper and/or lower layer arrangement. 11.The building panel according to claim 1, wherein each of said at leastone upper layer comprises a thermoplastic polymer and, optionally, afiller and/or wherein each of said at least one lower layer comprises athermoplastic polymer and, optionally, a filler.
 12. The building panelaccording to claim 1, wherein the at least one groove includes at leastone opening at a bottom-facing surface of the building panel.
 13. Thebuilding panel according to claim 1, wherein the at least one groove isbounded by a panel portion located below the at least one groove.
 14. Athermoplastic-based building panel comprising: an upper layerarrangement and/or a lower layer arrangement, a balancing layercomprising a thermoplastic polymer, and a mechanical locking system forhorizontally and/or vertically locking the building panel to an adjacentbuilding panel, the mechanical locking system comprising a cooperatingsurface provided in an edge portion of the building panel and beingconfigured to cooperate with a cooperating surface of the adjacentbuilding panel, wherein the cooperating surface of the mechanicallocking system is at least partially situated in the balancing layer.15. The building panel according to claim 14, wherein the balancinglayer is provided between said lower layer arrangement and said upperlayer arrangement.
 16. The building panel according to claim 14, whereinthe balancing layer is a bottom layer of the building panel.
 17. Thebuilding panel according to claim 1, wherein the balancing layer atleast partially extends through a locking element provided on a stripand/or through a locking groove, the locking element being configured toengage with the locking groove of said adjacent building panel forhorizontal locking.
 18. The building panel according to claim 17,wherein the cooperating surface is situated on the locking elementand/or in the locking groove.
 19. The building panel according to claim1, wherein the balancing layer at least partially extends along a stripand wherein an uppermost surface of the strip comprises a portion of thebalancing layer, said cooperating surface preferably being provided inthe uppermost surface.
 20. The building panel according to claim 1,wherein the balancing layer at least partially extends through a tongueportion, the tongue portion being configured to engage with a tonguegroove of the adjacent building panel for vertical locking.
 21. Thebuilding panel according to claim 20, wherein the cooperating surface issituated on the tongue portion.
 22. The building panel according toclaim 1, wherein the cooperating surface is a locking surface configuredto engage with a locking surface of the adjacent building panel in alocked state of the building panel and the adjacent building panel. 23.The building panel according to claim 1, wherein the cooperating surfaceis a guiding surface configured to guide the adjacent building panelduring locking of the building panel to the adjacent building panel.